1. Field of the Invention
This invention relates in general to a wireless communication systems, and more particularly to a method and apparatus for speeding up AAL2 connection setup during handover in advanced cellular networks.
2. Description of Related Art
The demand by consumers all over the world for mobile communications continues to expand at a rapid pace and will continue to do so for at least the next decade. Over 100 million people were using a mobile service by the end of 1995, and that number is expected to grow to 300 million by the year 2000. Several factors are contributing to the exciting growth in the telecommunications industry. For example, a combination of technology and competition bring more value to consumers. Phones are smaller, lighter, had a longer battery life, and are affordable now for the mass market. Operators are providing excellent voice quality, innovative services, and roaming across the country or world. Most important, mobility is becoming less expensive for people to use. Around the world, as well as in the United States, governments are licensing additional spectrum for new operators to compete with traditional cellular operators. Competition brings innovation, new services, and lower prices for consumers.
The basis for any air interface design is how the common transmission medium is shared between users, that is, the multiple access scheme. In frequency division multiple access (FDMA), the total system bandwidth is divided into frequency channels that are allocated to the users. In time division multiple access (TDMA), each frequency channel is divided into time slots and each user is allocated a time slot. In CDMA, multiple access is achieved by assigning each user a pseudo-random code (also called pseudo-noise codes due to noise-like auto-correlation properties) with good auto- and cross-correlation properties. This code is used to transform a user""s signal into a wideband spread spectrum signal. A receiver then transforms this wideband signal into the original signal bandwidth using the same pseudo-random code. The wideband signals of other users remain wideband signals. Possible narrowband interference is also suppressed in this process. TDMA and CDMA usually use FDMA to divide the frequency bank into smaller frequency-channels, which are then divided in a time or code division fashion.
There are several ways to classify CDMA schemes. The most common classification scheme is based on the modulation method used to obtain the wideband signal. This division leads to three types of CDMA: direct sequence (DS), frequency hopping (FH), and time hopping (TH). In DS-CDMA, spectrum is spread by multiplying the information signal with a pseudo-noise sequence, resulting in a wideband signal. In the frequency hopping spread spectrum, a pseudo-noise sequence defines the instantaneous transmission frequency. The bandwidth at each moment is small, but the total bandwidth over, for example, a symbol period is large. Frequency hopping can either be fast (several hops over one symbol) or slow (several symbols transmitted during one hop). In the time hopping spread spectrum, a pseudo-noise sequence defines the transmission moment. Furthermore, combinations of these techniques are possible.
Nevertheless, DS-CDMA is the technique that is being used for third generation wideband CDMA (WCDMA) proposals. Recently, extensive investigations have been carried out into the application of a code division multiple access (CDMA) system as an air interface multiple access scheme for IMT-2000/UMTS (International Mobile Telecommunications System 2000/Universal Mobile Telecommunications System). It appears that CDMA is the strongest candidate for the third generation wireless personal communication systems. As a result, many research and development (RandD) projects in the field of wideband CDMA have been going on in Europe, Japan, the United States, and Korea.
Wideband CDMA has a bandwidth of 5 MHz or more. The nominal bandwidth for all third generation proposals is 5 MHz. There are several reasons for choosing this bandwidth. First, data-rates of 144 and 384 Kbps, the main targets of third generation systems, are achievable within 5 MHz bandwidth with a reasonable capacity. Even a 2-Mbps peak rate can be provided under limited conditions. Second, lack of spectrum calls for reasonably small minimum spectrum allocation, especially if the system has to be deployed within the existing frequency bands occupied already by second generation systems. Third, the 5-MHz bandwidth can resolve (separate) more multipaths than narrower bandwidths, increasing diversity and thus improving performance. Larger bandwidths of 10, 15, and 20 MHz have been proposed to support higher data rates more effectively.
Several wideband CDMA proposals have been made for third generation wireless systems. These have all been proposed to provide advanced properties such as provision of multirate services, packet data, complex spreading, a coherent uplink using a user dedicated pilot, additional pilot channel in the downlink for beam-forming, seamless inter-frequency handover, fast power control in the downlink, and optional multi-user detection.
Today""s transmission protocols of many telecommunication networks are based on pulse code modulation (PCM), and mobile radio systems are no exception. The switching is also based on the switching of 64- or 56-Kbps PCM connections. ATM technology has received lot of attention during recent years as the next major transport technology. ATM has also been proposed for wireless applications (i.e., ATM cells are transmitted over the air interface).
ATM provides not only the multiplexing gains of packet switching, but also the guaranteed delay characteristics of circuit switching. The fundamental strategy behind ATM is to split the information into small fixed size units that are easy to handle. The fixed size of the cell allows efficient switching. ATM networks are high-speed switching systems offering large bit pipes, which allow statistical multiplexing (i.e., multiplexing of many connections with variable rate characteristics), which altogether reduces the overall bandwidth requirements. Since ATM is based on the transmission of fixed size cells, it can be easily evolved for future services.
The basic unit in an ATM is a cell of 53 bytes. The ATM cell consists of a header (5 bytes) and information fields (48 bytes). The header consists of a field for Generic flow control (GFC), Virtual path identified (VPI) and Virtual channel identifier (VCI). The VPI and VCI are used to identify the virtual path and virtual channels identified with that path to route the ATM cells from the source node to the destination node.
The ATM and the ATM adaptation layer (AAL) form the data link layer. AAL converts the arbitrarily formatted information supplied by the user into ATM cells. Various forms of AAL protocols are necessary to handle the different types of traffic. AAL0 provides direct access to the ATM layer. AAL1 assumes constant bit rate traffic, which is intolerant of mis-sequenced information and variation in delay. It offers the following function: segmentation and reassembly (SAR) handling of delay variation handling, handling of lost and mis-inserted cells, source clock recovery, monitoring for bit errors, and handling those errors.
AAL2 is used, for example, for voice and video. It assumes that traffic is bursty and intolerant of mis-sequencing and that a time stamp is needed for packet reassembling. It offers the following functions: multiplexing, SAR, handling delay variation, handling cell lost/error, and source clock recovery. AAL2 will be used for compressed speech in third generation mobile radio systems in the network infrastructure.
AAL3/4 and AAL5 are geared to traffic that has bursty characteristics with variable frame length. Furthermore, delay is not critical and packets can be resequenced based on sequence numbers. AAL5 is expected to supersede AAL3/4 since it has lower overhead and TCP/IP acknowledgments fit into one cell in AAL5 instead of two cells as in AAL3/4.
To meet the phenomenal growth in cellular communication and increasing demand for mobile multimedia services, cellular network providers are forging ahead to develop the third generation (3G) cellular network. Not so surprisingly in view of the characteristics described above, ATM is being considered as strong candidate for the Radio Access Network (RAN). ATM is a strong candidate for the RAN because it supports heterogeneous traffic types, provides Quality of Services (QoS) guarantee and is widely deployed in the carrier backbone networks. In order to meet the requirements specific to mobile communications such as transporting low bit rate compressed speech efficiently and within acceptable delay bounds, ITU-T has recently approved AAL2 to cater the needs of emerging multimedia cellular networks.
The use of ATM in 3G cellular access network has been further enhanced by the AAL2 signaling activities at the ITU-T. Mobility provides a seamless connectivity for a user and at the same time creates a number of problems for networks to maintain the connectivity. There have been many solutions available to tackle the problem and demonstrated for long time in GSM networks. However, this issue has been receiving considerable attention lately due to the QoS guarantee with mobility.
In 3G cellular access network, mobile telephony is carried over AAL2 to improve the resource utilization. To setup an AAL2 connection, the new AAL2 signaling protocol will be used. A connection request from a mobile terminal received at a Base Station (BS) initiates a AAL2 connection setup to the remote AAL2 peer entity located either in RAN or Core Network (CN). AAL2 connection setup involves negotiation of number of parameters such as traffic and QoS, codec selection, and maximum size of AAL2 packet. When a mobile user leave the Serving RNC (S-RNC) and enters a Drift RNC (D-RNC), the existing connection at the S-RNC has to be released and a new connection has to be established at the D-RNC. Setting up new AAL2 connection involves re-characterization of connection specific parameters and re-negotiation with the remote peer entity. This process will increase the handover delay and cause problem to the soft handover feature available in WCDMA based 3G networks.
AAL2 connections are originated from the BS (or S-RNC) instead of a mobile terminal in the 3G RAN. This separation of mobile call control and AAL2 connection control within the RAN adds complexity during the handover. Mobile terminals do not have any information related to the AAL2 connection within the RAN and cannot pass them to the new BS or D-RNC. The lack of information about the existing AAL2 connection at the D-RNC during handover will force the D-RNC to start the AAL2 connection setup all over again. This process will lead to re-negotiation of connection specific parameters with the peer entity and increase in delay during handover.
It can be seen that there is a need for a method and apparatus for decreasing overall handover delay when a user is moving from one coverage area to another coverage area in an ATM based advanced cellular radio access network.
It can also be seen that there is a need for a method and apparatus for speeding up AAL2 connection setup during handover in advanced cellular networks
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for speeding up AAL2 connection setup during handover in advanced cellular networks.
The present invention solves the above-described problems by bundling connection parameters for the current AAL2 connection and transferring in a single message for used in the new coverage area for a new AAL2 connection.
A method in accordance with the principles of the present invention includes requesting a new AAL2 connection from a destination access network to a remote AAL2 peer by a mobile terminal, initiating an AAL2 connection setup by the destination access network by sending a handover request to a serving access network, bundling AAL2 connection parameters associated with an old AAL2 connection by the serving access network, transferring the bundled AAL2 connection parameters to the destination access network and establishing a new AAL2 connection to the remote AAL2 peer connection by the destination access network using the transferred AAL2 connection parameters.
Other embodiments of a method in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the bundled AAL2 connection parameters is selected from the group comprising peak packet rate, burst tolerance, quality-of-service, codec selection, and maximum AAL2 packet size.
Another aspect of the present invention is that the transferring comprises encapsulating the AAL2 connection parameters within signaling messages used between the serving access network and the destination access network.
Another aspect of the present invention is that the method further includes clearing the old AAL2 connection.
Another aspect of the present invention is that the method further includes sending a connection success signal from the destination access network to the serving access network, clearing the old AAL2 connection, and sending a confirm signal from the serving access network to the destination access network.
Another aspect of the present invention is that the serving access network is a Base Station.
Another aspect of the present invention is that the destination access network is a Base Station.
Another aspect of the present invention is that the serving access network is a radio network controller.
Another aspect of the present invention is that the destination access network is a radio network controller.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.